A gate valve, also known as a sluice valve, is a valve that opens
by lifting a round or rectangular gate/wedge out of the path of the
fluid. The distinct feature of a gate valve is the sealing surfaces
between the gate and seats are planar. The gate faces can form a
wedge shape or they can be parallel. Typical gate valves should
never be used for regulating flow, unless they are specifically
designed for that purpose. On opening the gate valve, the flow path
is enlarged in a highly nonlinear manner with respect to percent of
opening. This means that flow rate does not change evenly with stem
travel. Also, a partially open gate disk tends to vibrate from the
fluid flow. Most of the flow change occurs near shutoff with a
relatively high fluid velocity causing disk and seat wear and
eventual leakage if used to regulate flow. Typical gate valves are
designed to be fully opened or closed. When fully open, the typical
gate valve has no obstruction in the flow path, resulting in very
low friction loss.
Solid and Flexible Wedge
Gate valves are characterized as having either a rising or a
non-rising stem. Rising stems provide a visual indication of valve
position. Non-rising stems are used where vertical space is limited
Bonnets provide a leak proof closure for the valve body. Gate
valves may have a screw-in, union, or bolted bonnet. Screw-in
bonnets are the simplest design, offering a durable, pressure-tight
seal. Union bonnets are suitable for applications requiring
frequent inspection and cleaning. They also give the body added
strength. Bolted bonnets are used for larger valves and higher
Another type of bonnet construction in a gate valve is a pressure
seal bonnet. This construction is adopted for valves for high
pressure service, typically in excess of 15 MPa (2250 psi). The
unique feature about the pressure seal bonnet is that the body
bonnet joint seals improve as the internal pressure in the valve
increases, compared to other constructions where the increase in
internal pressure tends to create leaks in the body-bonnet joint.
Carbon steel or stainless steel + flexible graphite combined gasket
is used for Class150 gate valve; stainless steel + flexible
graphite spiral wound gasket for Class 300 gate valve; stainless
steel + flexible graphite spiral wound gasket for Class 600 gate
valve, and ring type joint gasket is optional for Class 600 gate
valve; ring type joint gasket is used for Class 900 gate valve;
pressurized seal design is used for Class1500 to Class 2500 gate
Hand wheel or gearbox operator are usually applied, if required,
chain wheel is available. Top flange dimension according to ISO
5211 is available for valves to be actuated.
Belleville Spring Loaded Packing
If required, Belleville spring loaded packing can be applied to
enhance the durability, reduce fugitive emissions and increase
reliability of the packing seal.
Molded flexible graphite is normally used for packing material.
PTFE or combined packing material can be also adopted if required.
The internal surface of the stuffing box, of which area contacts
the packing, is fine finished (Ra 3.2μm). The stem surface,
contacting the packing, should be rolled and pressed after being
precisely machined, so as to reach to high finish and compactness
(Ra 0.8μm) and to ensure the reliable tightness of the stem area.
All FBV gate valves have a back seating design. In most cases, the
carbon steel gate valve is fitted with a renewable back seat while
for stainless steel gate valves, the back seat is machined directly
in the bonnet or is machined after welding. When the gate valve is
at fully open position, the sealing of the back seat is very
reliable. However, according to API 600, the packing shall not be
added or changed under line pressure.
For carbon steel gate valves, the seat material is usually forged
steel. The sealing surface of the seat is overlay welded with hard
alloy specified by the customer. Renewable threaded-in seat rings
are used for gate valves NPS≤10, and welded-on seat rings are
optional and can be used if required. Welded-on seats are used for
carbon steel gate valves NPS ≤10. For Stainless steel gate valve,
the seat is integral or hard alloy welded integrally to the body.
Threaded-in seat ring or welded-on seat is also optional for
stainless steel gate valves.
The stem is of one-piece wrought material, welding fabricated is
not permitted for FBV valves. The connection of the stem to the
disc is “T” type. The strength of the connecting area is higher
than that of the T threaded part of the stem. The strength test of
the area conforms to API 591.
Usually, the stem nut is made of copper alloy or ASTM A439 D2. For
large sized gate valves (NPS 10 for Class 150, NPS 8 for Class 300,
NPS 6 for Class 600, NPS 5 for Class 900), a roller bearing is
fitted underside of the stem nut in order to minimize the opening
and closing torque of the gate valve.